1. Field of the Invention
The present invention relates to a vehicle automatic transmission.
2. Description of the Related Art
Japanese Patent No. 4088566 discloses an automatic transmission that includes an input shaft, an intermediate shaft, a countershaft, an output shaft, a plurality of clutches capable of coupling gears rotatably supported on the input shaft, the intermediate shaft, and the countershaft to the shafts, and a selector (engagement unit) formed by a dog clutch capable of selecting coupling forward gears and a reverse gear rotatably supported on the countershaft to the countershaft. With this structure, the automatic transmission establishes a plurality of forward shift stages and a reverse shift stage.
When moving a shift lever from a D-position to an R-position via an N-position in the automatic transmission of the related art, or when moving the shift lever from the D-position to a P-position via the N-position and the R-position, a selector operates to couple the reverse gear to the countershaft so as to establish a reverse shift stage the moment the shift lever reaches the R-position.
In this case, in the automatic transmission of the related art, when the selector operates to couple the reverse gear to the countershaft, dog teeth of the reverse gear and dog teeth of the selector are sometimes not smoothly engaged, but are incompletely engaged, as will be described in detail in the following “DESCRIPTION OF THE EMBODIMENTS” of this specification. As a result, trouble occurs, for example, the dog teeth wear abnormally.
Accordingly, it is desirable to allow an engagement unit for coupling a reverse gear to a transmission shaft to smoothly operate when a shift position of an automatic transmission changes from a D-position to an R-position.